The proposed research is intended to address two specific areas presently under investigation: 1) the effects of environmental contaminants on fertilization, embryological development, recruitment (settlement and metamorphosis) and uptake of algal symbionts of mass-spawning corals; and 2) the genetic relationships among sympatric coral species and the genetic basis for hybridization among these sympatric species. These two related areasof study are the proposed focus of a continuing research effort and reflect the results of research accomplished under the previously funded NIH/MBRS program. These compatible studies will be undertaken to test the following hypotheses: 1) Certain reproductive and life-history stages of corals are more sensitive to environmental toxins than others; 2) The incorportion of symbiotic algae into coral recruits is affected by both genetic and environmental factors; 3) Natural hybridization has played a role in the diversification of corals. The three hypotheses will be tested using eggs, sperm, larvae, and tissue from selected species of mass-spawning corals. The first hypothesis will rely on bioassays investigating the effects of selected pesticides and polycyclic aromatic hydrocarbons (PAH's) on adult corals, egg-sperm interactions, larval development, and metamorphic induction. The second hypothesis will be tested using asymbiotic coral recruits and zooxanthellae extracted from conspecifics as well as corals of different genera, and under conditions of altered water quality. The genetic questions will be addressed using Random Amplified Dpolymorphic DNA (RAPD's) to identify specific markers. The proposed reserch is designed to address questions regrding the effects of environmental contaminants, reproduction, metamorphic induction, cellular recognition, as well as genetic relationships among organisms where egg-sperm interactions can be experimentally manipulated. Invertebrate models allow for experimentation not easily performed on higher organisms, with results that can be interpreted for application to understanding aspects of human health and genetics.